Technical Field
Embodiments of this disclosure generally relate to a laminate-type power storage element that houses a power generating element in an exterior body formed of laminated films and an implementation method using the power storage element.
Related Art
As a form of a power storage element such as a primary battery, a secondary battery, and an electric double layer capacitor, there has been provided a laminate-type power storage element that seals together with an electrolytic solution a flat plate-shaped electrode body, including a sheet-shaped positive electrode and a sheet-shaped negative electrode, together with electrolyte in a flat-bag-shaped exterior body formed of laminated films. Since the laminate-type power storage element easily achieves both a large capacity and downsizing and thinning and is also excellent in heat radiation performance, the laminate-type power storage element has been conventionally used as a power supply for driving an electric vehicle, a hybrid vehicle, or a similar vehicle. Recently, utilizing the feature of being easily downsized and thinned, the laminate-type power storage element has been used as a power supply for an extremely thin electronic device (hereinafter, a thin electronic device) that incorporates a power supply, such as an IC card with a one-time password function and a display, an IC card with display, a tag, and a token (one-time password generator). Especially, an external dimension of a card type electronic device (card electronic device) compliant to a standard for IC card is specified by the standard, and the thinness is extremely thin, 0.76 mm. Therefore, the laminate-type power storage element is indispensable as a power supply for the card electronic device.
FIGS. 1A and 1B illustrate a laminated lithium primary battery as a general laminate-type power storage element. FIG. 1A is an external view of a laminate-type power storage element 1, and FIG. 1B is an exploded perspective view illustrating an outline of an internal structure of this power storage element 1. As illustrated in FIG. 1A, the laminate-type power storage element 1 has a flat plate-shaped appearance. An exterior body 11 formed of laminated films shaped into a flat rectangular bag internally seals a power generating element. In the laminate-type power storage element 1 illustrated here, distal end parts (24 and 34) of a positive electrode terminal plate 23 and a negative electrode terminal plate 33 are guided in an identical direction from one side 13 of the rectangular exterior body 11.
Next, the following describes a schematic structure of the laminate-type power storage element 1 with reference to FIG. 1B. FIG. 1B hatches some members and portions for easy distinction from other members and portions. As illustrated in FIG. 1B, the exterior body 11 internally seals an electrode body 10 together with electrolyte. The electrode body 10 is formed by laminating a sheet-shaped positive electrode 20 and a sheet-shaped negative electrode 30 via a separator 40. The positive electrode 20 is formed by disposing a positive electrode material 22 containing a positive-electrode active material over one principal surface of a positive electrode current collector 21 made of a metal plate and a metal foil. The negative electrode 30 is formed by disposing a negative electrode material 32 containing a negative-electrode active material over one principal surface of a negative electrode current collector 31 made of a metal plate, a metal foil, or a similar material. The electrode body 10 is configured by laminating and press-bonding the positive electrode 20 and the negative electrode 30 such that the respective electrode materials (22 and 32) are opposed via the separator 40 (or being welded to the separator 40). In this example, electrode terminal plates (23, 33), which are formed of a strip-shaped metal plate, metal foil, or similar material, are mounted to the respective electrode current collectors (21 and 31) of the positive electrode 20 and the negative electrode 30. Further, the tab leads 2 are used as the electrode terminal plates (23, 33). As is well known, the tab leads 2 are structured in a adhered manner while sandwiching with the insulating resin sealing material (hereinafter, tab film 4) a portion of the extending strip-shaped terminal lead 3. The terminal leads 3 here are substantially the electrode terminal plates (23, 33) made of metal plates, metal foil or the like. And respective end portions 5 of the terminal leads 3 are exposed outside the exterior body 11 as the distal end parts (24, 34) of the positive electrode terminal plate 23 and the negative electrode terminal plate 33. The other respective end portions are coupled to a part of the positive electrode current collector 21 and a part of the negative electrode current collector 31 by such as an ultrasonic welding method.
The exterior body 11 is configured by welding peripheral edge regions 12, which are hatched or indicated by the dotted line frame in the drawing, of two rectangular laminated films (11a and 11b), which are stacked to one another, by thermocompression bonding to seal the inside. As is well-known, the laminated films (11a and 11b) have a structure where one or more resin layers are laminated on front and back of a base material made of such as an aluminum foil. Generally, the laminated films (11a and 11b) have a structure where a protecting layer made of, for example, a polyamide resin is laminated on one surface and an adhesive layer with thermal weldability made of, for example, a polypropylene is laminated on the other surface. And when the laminate-type power storage element is assembled, the two laminated films (11a and 11b) are made to face each other with the adhesive layer sides facing the inside and the electrode body 10 being disposed between the two laminated films (11a and 11b). And the peripheral edge regions 12 of the two laminated films (11a and 11b) facing each other are thermocompression bonded to configure the flat bag shaped exterior body 11. The tab films 4 of the tab leads 2 at the margin 13 on the side where the electrode terminal plates (23, 33) protrude outward at the peripheral edge regions 12 of the exterior body 11 are thermally welded together with the laminated films (11a and 11b) during this thermocompression bonding. And hereby, the tab films 4 that are welded to the terminal leads 3 are further welded to the adhesive layer of the laminated films (11a and 11b) at this margin 13.
Since the laminate-type power storage element 1 is used as the power supply for electronic devices, to incorporate the laminate-type power storage element 1 into the electronic device, the electrode terminal plates (23, 33) need to be coupled to an electronic circuit in the electronic device. In other words, the laminate-type power storage element 1 needs to be implemented to the substrate of the electronic circuit (circuit board). Soldering, ultrasonic welding and the like can be given as methods for implementing the laminate-type power storage element 1. However, solder thickness control during soldering is difficult. When the laminate-type power storage element 1 is used in for example, the above card electronic device, the solder may become thick at the implementation region so that the laminate-type power storage element 1 may not be able to be incorporated into the card electronic device. On the other hand, the thickness of the implementation region would not present an issue with ultrasonic welding, since the electrode terminal plates (23, 33) themselves are directly welded to the predetermined print wiring part on the circuit board. However, since ultrasonic welding is associated with ultrasonic vibration caused by a large amount of energy creating frictional heat that melts the contact surface between the electrode terminal plates (23, 33) and the print wiring, the electrode terminal plates (23, 33) may be damaged or disconnected, depending on circumstances, in cases where the electrode terminal plates (23, 33) are formed with thin metal foils. Therefore, a method using an anisotropic conductive film (hereinafter also referred to as an ACF) has been widely employed as an implementation method for the laminate-type power storage element 1. As is well known, an ACF is a film-shaped component having a predetermined thickness used for implementation, and has a conductive property only in the thickness direction.
FIGS. 2A to 2D are schematic drawings illustrating the method for implementing the laminate-type power storage element 1 illustrated in FIGS. 1A and 1B to an electronic circuit board using the ACF. FIGS. 2A to 2D illustrate the implementation procedure. FIGS. 2A to 2D are enlarged views schematically illustrating a region near the electrode terminal plates (23, 33) of a cross section viewed from arrow a-a in FIG. 1A. First, as illustrated in FIG. 2A, the distal ends (24 and 34) of the electrode terminal plates (23, 33) are guided to the outside of the exterior body 11 in the assembled laminate-type power storage element 1. The positive electrode terminal plate 23 and the negative electrode terminal plate 33 are separately disposed in a direction orthogonal to the plane of the paper of FIG. 2A. As illustrated in FIG. 2 B, a single ACF 70 is interposed between a power feeding terminal pad 61 and respective surfaces of the distal end sides (24 and 34) of the electrode terminal plates (23, 33) of the positive electrode 20 and the negative electrode 30 (hereinafter also referred to as implementation surfaces 50). The power feeding terminal pad 61 is formed as a print wiring on a circuit board 60 such as a flexible printed circuit board (FPC) constituting the electronic circuit. That is, the one ACF 70, which extends in the direction orthogonal to the plane of the paper of FIGS. 2B to 2D, is bridged across the two electrode terminal plates (23, 33). As illustrated in FIG. 2B, the relative up-down direction of the electrode terminal plates (23, 33) is specified with the implementation surfaces 50 of the electrode terminal plates (23, 33) being disposed to become the lower surfaces. Then, as illustrated in FIG. 2C, the thermocompression bonding is performed from above the top surfaces (hereinafter also referred as back faces 51) of the electrode terminal plates (23, 33) with, for example, a block-shaped jig 80 having a built-in heater. As illustrated in FIG. 2D, this couples the electrode terminal plates (23, 33) of the two positive and negative electrodes to the power feeding terminal pad 61 on the circuit board 60 via the one ACF 70. The implementation method using the ACF 70 in this way can maintain the implementation region in a uniform thickness and the electrode terminal plates (23, 33) would not be damaged since the electrode terminal plates (23, 33) need not be vibrated as in the case of ultrasonic welding. And the laminate-type power storage element 1 can be implemented to the circuit board by the thermocompression bonding having a sufficiently large coupling strength and a sufficiently small coupling resistance. For example, the web page of FDK CORPORATION, Internet <URL: http://www.fdk.co.jp/battery/lithium/lithium_thin.html>(<URL: http://www.fdk.com/battery/lithium_e/lithium_thin.html> in English)), (“Thin Type Primary Lithium Batteries) describes a structure of the ACF 70, the implementation method using the ACF 70, or similar information. For example, Japanese Unexamined Patent Application Publication No. 2006-281613 discloses the structure of the laminate-type power storage element 1 or similar information. The above web page describes features, discharge performance, and a similar specification of the thin lithium batteries that are actually commercially available laminate-type power storage elements 1.
In order to implement the laminate-type power storage element 1 to the electronic circuit using the ACF 70, in accordance with the up-down direction illustrated in FIG. 2A to FIG. 2D, the jig 80 is pressed from above the electrode terminal plates (23, 33) to couple the electrode terminal plates (23, 33) to the circuit board 60 via the ACF 70. That is, the ACF 70 is heated via the electrode terminal plates (23, 33) made of metal having excellent thermal conductivity. The ACF 70 is thermally welded to the terminal pad 61 or a similar member on the circuit board 60. The jig 80 that comes into contact with the top surfaces of the electrode terminal plates (23, 33) may reach a temperature of 200° C. during the thermocompression bonding process. Hereby, the heat of the jig 80 is transmitted to the electrode body 10 inside the exterior body 11 via the electrode terminal plates (23, 33), possibly damaging the electrode body 10 by a so-called temperature shock. The heat of the jig 80 during thermocompression bonding the ACF 70 would transmit through the electrode terminal plates (23, 33) to the entire region of the small electrode body 10 inside the exterior body 11 in a short time creating a high possibility of damaging the electrode body 10. This is notable with the laminate-type power storage element 1 used as the power supply of a small-sized thin electronic device represented by a card type electronic device.
There is a laminate-type power storage element called a support-type laminate-type power storage element 1s which has one of the two laminated films (11a, 11b) that configure the exterior body 11 extended to the distal end regions (24, 34) of the electrode terminal plates (23, 33), as described in the above web page. FIGS. 3A to 3C illustrate this support-type laminate-type power storage element 1s. Similar to FIGS. 2A to 2D, the up-down direction is defined with the side of the implementation surfaces 50 of the electrode terminal plates (23, 33) facing the downward direction and the front-rear direction is defined with the direction in which the electrode terminal plates (23, 33) are guided outside as the front direction, in the following. The direction that is orthogonal to both the up-down and the front-rear directions is defined as the right-left direction, where each of the right and the left directions are designated when viewed from the front toward the rear, as illustrated in FIGS. 3A to 3C. FIG. 3A is an external view of the support-type laminate-type power storage element is seen from above, FIG. 3B is a perspective view of the support-type laminate-type power storage element is seen from below and FIG. 3C is a drawing enlarging a part proximate the electrode terminal plates (23, 33) of a cross section viewed from arrow b-b in FIG. 3A.
As illustrated in FIGS. 3A to 3C, the support-type laminate-type power storage element is has the locations of the front margins (13a and 13b) from which the electrode terminal plates (23, 33) are guided outside differentiated at the respective laminated films (11a and 11b) that face each other. In the example illustrated in FIGS. 3A to 3C, the lower laminated film 11b, similar to a common laminate-type power storage element 1 illustrated in FIGS. 1A and 1B, has the front margin 13b thereof located where the electrode terminal plates (23, 33) are guided outside, whereas the upper laminated film 11a has the front margin 13a thereof located at a position that covers the entire region where the electrode terminal plates (23, 33) are formed. In other words, the upper laminated film 11a extends up to a location such that the entire region where the electrode terminal plates (23, 33) are formed is covered by the right and left margins 14. And a rectangular region (hereinafter also referred as support tab 15) that alone covers the back faces 51 of the electrode terminal plates (23, 33) is formed to the front margin 13b of the lower laminated film 11b. The electrode terminal plates (23, 33) and the ACF 70 are thermocompression bonded from above the support tab 15 as illustrated in FIG. 4 when implementing this support-type laminate-type power storage element 1s. Hereby, the electrode terminal plates (23, 33) do not come into direct contact with the jig 80 thereby keeping the temperature of the electrode terminal plates (23, 33) from suddenly rising and enabling the electrode body 10 from being damaged.
By the way, the support tab 15 is a part of the laminated film 11a and the side thereof that faces the back faces 51 of the electrode terminal plates (23, 33) has formed thereto an adhesive layer that melts by heat. And during thermocompression bonding, the adhesive layer of the support tab 15 comes into contact with the back face 51 of the electrode terminal plates (23, 33) and heat concentrates on the metal electrode terminal plates (23, 33) as well. Therefore, the region of the adhesive layer of the support tab 15 that comes into contact with the electrode terminal plates (23, 33) during thermocomporession bonding melts faster than the other regions so that the melting of the adhesive layer may reach up to the surface layer of the metal foil, which is the base of the laminated film 11a. When the adhesive layer of the laminated film 11a melts up to the surface layer of the metal foil in the region where the adhesive layer of the of the laminated film 11a comes into contact with the back faces 51 of the electrode terminal plates (23, 33), it is a matter of course that a short-circuit would be developed between the electrode terminal plates (23, 33) of the positive electrode 20 and the negative electrode 30.